Promycelium in rust fungi bears

Promycelium in rust fungi bears Basidiospores.
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales.
Rust fungi require two unrelated hosts to complete their life cycle, with the primary host being infected by aeciospores and the alternate host being infected by basidiospores.
They usually do not infect a plant directly, instead, they germinate to produce basidia and basidiospores. Basidiospores are windborne haploid spores that often infect the alternate host in Spring.